I see a humongous loophole or series of them. Charlie was a minor, making his parents liable. Demonic immunity.
Contributory negligence. Succubus lures impaired minor into unprotected sex.
Zereth is the same calculating bastard who uses and discards his children as tools. Sev is the current tool.
The kiss with Caelo got to him. I also doubt he can kill Ember.